Intraplate Volcanism of the Alba Guyot: Geodynamic Formation Models of the Magellan Seamounts in the Pacific Ocean for 100 million years

Abstract

Abstract -We report data on 9 samples of basaltic rocks and a spinel lherzolite xenolith collected during dredging in the area of Alba Guyot (Magellan Seamounts, Pacific Ocean). The data include 40Ar–39Ar ages of five samples and mineral chemistry of rock-forming and accessory minerals and glasses, with implications for the formation conditions of Ti-amphibole in basaltic melts. The upper slope parts at Alba Guyot and its satellite Oma Vlinder at sea depths of 3600 to 2200 m, are composed of ~1400 m thick basaltic rocks that formed within the 112 to 86 Ma interval (40Ar–39Ar plateau ages). Later, in its 60 Myr history postdating the Cretaceous volcanism, the guyot was exposed to erosion, which produced a plateau-like flat top, and underwent another pulse of volcanism in the Cenozoic. Miocene (<20 Ma) eruptions of basanitic magma on the Alba Gyot plateau were associated with petit-spot volcanoes. Judging by the absence of hyaloclastic deposits around those volcanoes and the age of the lavas, the Cenozoic eruptions occurred in subaerial conditions before the guyot submerged below the sea level. The Alba volcanics have greater contents of incompatible elements than typical oceanic island basalts (OIB), apparently, because they formed by low-degree partial melting of different sources: pargasite-bearing spinel peridotite of the metasomatized oceanic lithosphere, mainly for Cretaceous basaltic rocks, and/or garnet peridotite for Miocene petit-spot basanites. Multiple eruptions at Alba Guyot for 100 Myr may have been maintained either by the Southern Pacific Superplume in the region of the South Pacific Thermal and Isotopic Anomaly (SOPITA) in the Mesozoic or by translithospheric faulting originated at the lithosphere-asthenosphere boundary (LAB) in the Cenozoic.